The intermediate-affinity interleukin (IL) 2 receptor expressed on Theileria annulata-infected cells comprises a single IL 2-binding protein. Partial characterization of bovine IL 2 receptors

Bovine high-, intermediate- and low-affinity interleukin 2 receptors (IL2R) were studied by ligand binding and affinity labeling using 125I-labeled IL 2 and homobifunctional chemical cross-linking reagents. High- (Kd = 17 pM) and low-affinity (Kd > 6 nM) IL2R were detected on concanavalin A-activated peripheral blood lymphocytes (PBL). Theileria annulata (TA)-infected autonomously growing PBL (TA-PBL) express predominantly intermediate-affinity IL2R (Kd = 1 nM). Affinity-labeling studies revealed that the high-affinity IL2R comprises a 55-kDa (L chain) and an additional 90-kDa IL 2-binding protein (H chain). TA-PBL express predominantly the H chain. In contrast to the human chain, the bovine form was not separable by sodium dodecyl sulfate-polyacrylamide gel electrophoresis/urea into the two distinct bands H1 and H2 and ran in parallel to the human H2 band. These results suggest (a) that the bovine intermediate-affinity IL 2R comprises a single H chain and (b) that the single H chain and the L chain are sufficient to form the functional high-affinity bovine IL2R.